The present invention relates to a vacuum envelope effective to various devices where field emission elements, each emitting electrons in an electric field, are arranged within the vacuum envelope. Particularly, the present invention relates to an electrode leading structure in a vacuum envelope for photoelectric conversion elements or displays employing field emission devices (FEDs) being flat-emission-type cold cathode ray tubes fabricated by the semiconductor micro-processing technology.
The Spindt-type field emission cathodes (FECs) are now in the practical stage as field emission elements fabricated by fully using the semiconductor technology and are well employed for displays.
FIG. 7 schematically illustrates the configuration of a Spindt-type cathode field emission cathode. This perspective view shows a field emission cathode manufactured using the semiconductor micro-processing technology.
Referring to FIG. 7, a cathode k is vapor-deposited on the substrate S. Cone emitters E are formed on the surface of the cathode K. A gate GT is formed over the cathode K via the insulating layer of a silicon dioxide (SiO2). The cone emitters E are respectively formed within holes opened in the gate GT. The tips of the cone emitters E are respectively viewed from the openings of the gate GT.
The micro-processing technology is employed to fabricate the cone emitters E arranged with pitches of less than 10 microns. Field emission cathodes of several ten thousands to several hundred thousands can be formed on a single substrate S.
Since the space between the gate GT and a cone emitter E can be set to the order of sub-microns, the emitter E field-emits electrons with several ten volts Vgk applied between the gate GT and the cathode K.
The anode A is spaced from the gate GT by a predetermined distance. The anode A can attract electrons emitted from the emitter E with the anode voltage Va applied. A fluorescent substance (not shown) coated over the anode A is excited by the accelerated electrons so that the display becomes a glow state.
With the photoelectric conversion layer film stacked over the anode A, the anode current depends on the light amount externally applied. An image pickup can detect the anode current.
In the conventional field emission display shown in FIG. 7, the space between the gate GT and the anode A is the order of several hundred micrometers. Such a field emission device allows a very thin vacuum envelope to be fabricated.
FIG. 8 is a cross sectional view partially illustrating the main portion of the flat vacuum envelope.
Referring to FIG. 8, a first glass substrate 11 has a field emission portion 11a formed of emitters E and the gate GT. A second glass substrate 12 has an anode 12a which has a laminated layer of a fluorescent display substance and a transparent electrode acting as a conductive metal-back layer. A side wall portion 13 surrounds the space between the first glass substrate 11 and the second substrate 12 to maintain a vacuum state. Normally, the side wall portion 13 is constructed slightly larger to define a getter room. The end portions of the side wall portion are joined with the first glass substrate and the second glass substrate using the fritted glass 14 so that the inside thereof is maintained in a vacuum state.
Numeral 13a represents an exhaust hole attached to evacuate the vacuum envelope to a vacuum state. The exhaust tube 13b externally attached to the exhaust hole 13a is used to evacuate the inside the vacuum envelope. The vacuum envelope is fabricated by sealing the exhaust tube 13a. 
The side wall section 13 has a hole 13c through which the lead 15 passes to be in contact with the anode 12a. 
With the lead 15 penetrating the hole 13c, the side wall portion 13 is securely fixed with the crystallized glass 13d while the spring member 15a formed at the front end of the lead 15 is resiliently contacted to the anode 12a. Thus, a relatively high voltage can be applied to the anode 12a. 
A relatively-low drive voltage applied to the field mission portion 11a on which the emitters E and the gate GT are formed can be externally applied via a great number of transparent conductive films printed on the first glass substrate 11 (not shown).
According to the flat vacuum envelope mentioned above, the lead 15 is in direct contact with the anode 12a and is drawn outside thereof, so that the contact between the anode 12a and the lead 15 becomes unstable. This causes a frequent contact failure or a self-discharge occurs when a high voltage of, for instance, several kilovolts is applied to the anode.
Particularly, the conductivity between the front end of the lead 15 and the anode 12a is achieved with the contact pressure of the spring member 15a of the front end after the sealing of the side wall portion 13. However, the conductivity may be impaired because of impact during fabrication or mechanical shock after fabrication. This results in poor manufacturing yields and poor product reliability.
The present invention is made to solve the above-mentioned problems.
Moreover, the objective of the invention is to provide a flat vacuum envelope where an anode electrode can be connected to the high-voltage supplying electrode with high reliability.
The objective of the present invention is achieved by an electrode structure within a flat vacuum envelope comprising a first glass substrate on which field emission cathodes are arranged on a surface thereof; a second glass substrate on which an anode electrode to attract electrons emitted from the field emission cathodes, the second glass substrate being confronted with the first glass substrate, a space between the first glass substrate and the second glass substrate being maintained in a vacuum state; a connection electrode plate placed on the anode electrode and acting as a conductive metal plate; and a lead connected to the connection electrode plate and externally extended through the first glass substrate or the vacuum envelope.